SeaKing Stores › 4mm cobalt HSS-CO jobber drill bit - EACH 4mm cobalt HSS-CO jobber drill bit - EACH £4.40 4mm diameter cobalt HSS-CO jobber drill bit. Sold individually, not as the purchase pack. Supplier reference: HSSCO4. Add To Cart Added! 4mm diameter cobalt HSS-CO jobber drill bit. Sold individually, not as the purchase pack. Supplier reference: HSSCO4.